1. Field of the Invention
This invention relates to an improved electrophotographic photosensitive member and more particularly to an electrophotographic photosensitive member containing a pyrazoline compound suitable as a charge-transporting material, the photosensitive member comprising a charge generation layer and a charge transport layer.
2. Description of the Prior Art
There have so far been known inorganic photoconductive materials such as selenium, cadmium sulfide, zinc oxide, etc. as photoconductive materials used for electrophotographic photosensitive members. In contrast to their many advantages, for instance, chargeability to a suitable potential in a dark place, slight dissipation in a dark place, and capability of dissipating rapidly charge by light irradiation, these photoconductive materials have various disadvantages, for example, as follows: in the case of selenium type photosensitive members, the crystallization of the photoconductive materials readily proceeds under the influence of surrounding factors such as temperature, moisture, dust, and pressure, in particular remarkably when the surrounding temperature exceeds 40.degree. C., thus resulting in lowering of chargeability or white spots in image. In the cases of these photosensitive members and cadmium sulfide type photosensitive members, stable sensitivity and durability cannot be obtained in repeated operations under high humidity conditions. In the case of zinc oxide type photosensitive members, which require sensitization by a sensitizing pigment, Rose Bengal being a typical sensitizing pigment, stable images cannot be obtained over a long period of time, since the sensitizing pigment tends to cause charge deterioration by corona discharge and light fading by exposure to light.
On the other hand, various kinds of organic photoconductive polymers have been proposed the first of which was polyvinylcarbazole. However, although excellent in film forming properly, in lightness, and in some other points as compared with said inorganic photoconductive materials, these polymers have until now failed to be put to practical use, by reason that they are still unsatisfactory in film forming property and inferior to the inorganic photoconductive materials in sensitivity, durability, and stability to change of environmental conditions.
Such being the case, in recent years laminated members have offered which comprise two layers provided with separate functions, that is, a charge generation layer and a charge transport layer which contains an organic photoconductive materials. Electrophotographic photosensitive members comprising such photoconductive layers of laminate structure have been improved in certain points such as sensitivity to visible light, charge bearing capacity, and surface strength, in which photosensitive members employing organic photoconductive materials had been deficient. Such improved electrophotographic photosensitive members have been disclosed, for example, in U.S. Pat. No. 3,837,851 (Japanese Pat. Appl. Laid-open No. 105537/1974), U.K. Pat. No. 1,453,024 (Japanese Pat. Appl. Laid-open No. 90827/1976), and U.S. Pat. Nos. 3,484,237 and 3,871,882.
Electrophotographic photosensitive members employing existing organic photoconductive materials are however still unsatisfactory in sensitivity and disadvantageous in that notable variations of surface potential are caused by repeated charging and exposure, and in particular an increase in light area potential and a decrease in dark area potential are remarkable in that case.